PERFORM VERIFICATION/CALIBRATION OF THE
INTER-ORAL DENTAL X-RAY
To ensure that the Heliodent 70 portable dental x-ray unit remains safe to
operate and functions properly, the x-ray requires verification/calibration. You must
perform this task at least annually. Refer to paragraph 1-2 for a list of equipment you
need to calibrate the x-ray unit. This lesson covers the following three
verification/calibration tasks: verifying adequacy of the power supply, calibrating the
dvm, and verifying/ calibrating exposure time.
When performing verification/calibration refer to figures 2-1, 2-2, 2-3, 2-4, and
2-5 for device acceptable performance parameters. Measurement base of technique
factors are as follows below.
a. Kilovolt (kv) measurements were obtained using an oscilloscope with
frequency compensated bleeder resistors and a spectrum analyzer.
b. Tube current was measured by a dcma meter, accuracy 1.5 percent accuracy
at full scale.
c. The exposure time was measured with an oscilloscope, and determined using
the time of high-voltage without the pre-heat time.
d. The cooling curve for the tube housing is steeper than is the curve for the
anode because it is measured in 104, not 103 heat units (HU). Since the curve is
steeper, even though the anode cools in a shorter period of time, the absolute rate of
cooling for the tube housing is greater.
e. When making x-rays, do not exceed the maximum cumulative HU. For
example, if you make a series of exposures totaling 5000 HU and are required to repeat
the series, you must wait a minimum of 2 minutes before repeating the series. In 2
minutes the unit will retain slightly less than 2000 HUs; repeating a series generating
5000 HUs will raise the cumulative HUs to slightly less than 7000 (2000 remaining HU
from the original exposures + 5000 new HUs from the repeat exposures).